How do you fill a gap between the shower tray and wall?

Ideally the tiling would come down over the edge of the shower tray but if your walls are really out of square,you can get sealing strips to go around the join between wall and tray.

Hi, I think I understand your problem, the tray is smaller than the opening leaving you a gap. The best way round this kind of situation is to construct a timber frame to fill the gap, then silicone the the timber frame at the joints between the wall and shower tray. Then apply a suitable sealant for tiling, and tile onto the section overlapping the shower tray and apply a slight fall to the tray.

There is no real option here. I'm assuming your walls are not square, and this makes it impossible to put the tray tight against the walls... You need to chop out some of the wall, pushing the tray into the recess, so that when you tile, the bottom course rests on top of the shower tray. (Doesn't hurt to squeeze a load of silicone between the wall and the tray as you fit it too.... hold the tray firmly and helps keep water from leaking below.) HOWEVER - it is vital that you confirm that the shower enclosure will still fit comfortably once the tiling is complete... some cubicles have very small tolerances and chopping out the wall to get the tray square can sometimes compromise this final stage of the installation...

I agree with Rok, is there no way of moving the shower tray over or building the wall out?

there should not be a gap the tiles should have been laid after the tray was fitted, if it is too late then your only solution is half a tonne of silicone

should have bonded your walls out first ,i love d i y cant understand why you try to do something you know nothing about ,i wouldnt try and programme a computer ,get someone in ie bathroom fitter and do it right d i r lol it will be cheaper in the long run believe me